Fiber component/resin component composite structural parts are presently formed by injection molding of the resin component into a mold containing the preformed fiber component. The mold cavity containing the fiber preform will be evacuated prior to injecting the resin into the mold cavity; however, present methods nevertheless encounter problems in ensuring that the fiber preforms are completely encased and saturated by the resin, and that the resultant parts are "net molded" parts, i.e., that the resin is able to completely fill the mold cavity so that minimal post molding modification of the resultant parts is necessary. It is highly desirable to produce net molded parts because of the relatively fragile nature of the fiber preforms, and their tendency to disintegrate when subjected to excessive post molding rework. The reason for this fiber preform structural fragility is that the preforms, while exhibiting very high tensile strength, are essentially only two-dimensional woven sheets of cloth, or merely two-dimensional sheets of parallel fiber strands. These preforms possess negligible through-plane strength or cohesion.
The problem that causes the difficulty in producing the net molded final parts is that the resin, when injected into the mold containing the fiber preforms, must move through the mold cavity in the in-plane direction of the fiber preforms, since the preforms will in many cases be arranged parallel to the direction of flow of the incoming resin so that the resin will have to flow from one end of each fiber preform sheet to the other end (or in the "in plane" direction of the preforms) in order to fill the mold cavity. At the same time, the resins used in forming such articles are usually thermosetting resins and will tend to begin setting up relatively quickly after their complimentary components are brought together in a premix chamber, or in the mold cavity once the proper temperature has been reached. Thus, it is difficult to ensure that the fiber preforms will be thoroughly saturated with the resin, and that the resin will completely fill the mold cavity, so as to produce a net molded part that requires little or no subsequent modification.
It would be desirable to be able to increase the pressure head or force throughout the entire procedure with which the resin is caused to flow through the preforms and mold cavity, over and above that which results from pressurizing the resin components, and depressurizing the mold cavity, as are presently done.